Backside Illumination (BSI) image sensor chips are replacing front-side illumination sensor chips for their higher efficiency in capturing photons. In the formation of the BSI image sensor chips, image sensors, such as photo diodes, and logic circuits are formed on a silicon substrate of a wafer, followed by the formation of an interconnect structure on a front side of the silicon chip. The wafer is then thinned, and backside structures such as color filters and micro-lenses are formed on the backside.
The image sensors in the BSI image sensor chips generate electrical signals in response to the stimulation of photons. The magnitudes of the electrical signals (such as the currents) depend on the intensity of the incident light received by the respective image sensors. Conventional formation process of BSI image sensor chips suffer from optical cross-talks between the light received by different image sensors.